Top 5 Most Damaging Invasive Species in the U.S.

Animal invaders have bridged oceanic gaps for centuriessome stowed away in ships while others were intentionally lugged over by the overzealous. Here are the most damaging animals ever to enter U.S. soil.

Animal invaders have bridged oceanic gaps for centuries—some stowed away in ship-ballast water while others were intentionally lugged over by the overzealous, either to solve a pre-existing problem or just for aesthetic pleasure. However, sometimes a seemingly benign introduction creates environmental travesty and ecosystem despair. Here are the most damaging animals ever to enter U.S. soil.

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Starlings

"Invasive species have been a problem as long as America has existed as a nation," says Thom Cmar of the Natural Resources Defense Council (NRDC). However, Cmar says that as transportation into the country has become more advanced, more invasive species have come in on boats and planes, thus worsening the problems posed to ecosystems.

These species have the uncanny knack of muscling out local competitors in the U.S., sometimes pushing commonplace species onto the endangered list by outcompeting them for food or resources. And as these creatures perpetually vandalize ecosystems, the U.S. has to shell out the money to fix the messes and restore nature's balance. Removing organisms that are numerous and evasive is no easy task, similar to finding a needle in a haystack, and so the U.S. focuses its efforts on border patrol, ensuring that no more of these species enter the country.

The NRDC advocates closing the routes that invasive species often use to hitchhike into the country, while the U.S. Fish and Wildlife Service, under the Lacey Act, regulates what people are legally allowed to bring in to the U.S.

"The costs of invasive species are so high, literally hundreds of billions of dollars a year," Cmar says. "Allowing these species to continue to come in and devastate our economy and ecology isn't an acceptable solution."

Of all the invaders, here are the worst of the worst, those that seem to be guests in the U.S. for the long haul, regardless of plans devised to be rid of them.

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Constrictors

Big constrictors squeeze the life out of mammalian prey and ecosystems. The U.S. Geological Survey says nine species of pythons, a type of snake that can range from 12 to 28 feet in length, pose a medium- to high-risk threat to ecosystem health. Over the past 30 years, these weighty reptiles have been traded domestically and internationally, and pet owners often take these snakes into homes that cannot accommodate them as they grow. When the snakes get too big, offending owners release them into the typically Floridian wild, where they ingest endangered species like the Key Largo wood rat and invade wildlife refuges. Under the Lacey Act, the U.S. Fish and Wildlife Service proposed to stop constrictor serpent imports into the country and even ban transport between states.

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Asian Carp

Many injurious invasives come by water. Asian carp—including the common, black and bighead variety—were brought to the U.S. in the 1970s as live vacuum cleaners meant to remove algae and suspended matter from ponds. These fish can grow to 100 pounds and will eat just about anything, adapting shockingly well to new environments. They have taken over and now represent 90 percent of the biomass in the Illinois River. Researchers worry that these ravenous, opportunistic fish will reach the Great Lakes and cause real problems to the fragile ecosystem—virtually eliminating biodiversity.

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Zebra Mussels

Zebra mussels originally smuggled their way into the U.S. in the ballast water of boats and have clogged the inside of pipes since the 1980s. These are no minor pipe blockages—these clogs total billions of dollars in fixes. And the mussels cling to more than pipes. They adhere to motors and to other native mussels, wreaking havoc for boat owners and decimating indigenous wildlife. So many zebra mussels exist in the Great Lakes, constantly filtering water, that they've changed the water from murky to clear, fiddling with the careful ecosystem balance. With clearer water, more sunlight reaches the bottom of the lakes where organisms thrive on darkness and can't live in the light.

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Mongoose

The small Indian mongoose, reaching no more than a foot or two in height, was originally brought to Puerto Rico and the Hawaiian islands to protect sugar cane fields from rat and snake damage. But instead of acting as an aid for crowd control, the mongoose quickly became a hindrance, harming far more wildlife than anticipated. Now fully settled in Hawaii, the agile creature preys on birds and small reptiles, which injures both the poultry industry and game hunters and costs the island nations $50 million dollars in damages a year. The mongoose has so far caused the extinction of 12 reptile and amphibian species from Puerto Rico, the West Indies and Jamaica.

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Starlings

This innocuous, petite speckled migrant came to the U.S. in the late 1800s as part of a misguided attempt to introduce the animals mentioned in Shakespeare's works to America. Like Shakespeare's works, European starlings stuck in the U.S. and disseminated outward from New York City, where they originally arrived. Now starlings occupy most of North America, steal nesting sites from other birds and rob the agriculture industry of $800 million dollars annually by damaging fields. To make matters worse, starlings spread diseases that infect both humans and livestock, costing a further $800 million a year in healthcare.

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